S-GW Relocation with Same SGW-U

The following illustration describes the S-GW relocation with destination S-GW selecting the same UPF.

S-GW Relocation with Same SGW-U Call Flow Description
Step Description
1

As part of initial attach, N4 and Sxa session is already established with Source SGW-C/cnSGW, SMF/IWF, and UPF.

The MME sends Create Session Request to the destination SGW-C/cnSGW.

2 The destination SGW-C/cnSGW sends Sx Establishment Request (Sxa) to the UPF. The UPF links new Sxa session with the N4 session for uplink packets (Slowpath).
3 The UPF sends Sx Establishment Response (Sxa) to the destination SGW-C/cnSGW.
4 The destination SGW-C/cnSGW sends Create Session Response to the MME.
5 The MME sends Modify Bearer Request (eNodeB F-TEID) to the destination SGW-C/cnSGW.
6 The destination SGW-C/cnSGW sends Sx Modify Request (Sxa) to the UPF.
7 The UPF sends Sx Modify Response (Sxa) to the destination SGW-C/cnSGW.
8 The destination SGW-C/cnSGW sends Modify Bearer Request to the SMF/IWF.
9 The SMF/IWF sends Sx Modify Request (N4) to the UPF. The UPF switches downlink tunnel and links the N4 session with the new Sxa session.
10 The UPF sends Sx Modify Response (N4) to the SMF/IWF.
11 The SMF/IWF sends Modify Bearer Response to the destination SGW-C/cnSGW.
12 The destination SGW-C/cnSGW sends Modify Bearer Response to the MME.
13 The MME sends Delete Session Request to the source SGW-C/cnSGW.
14 The source SGW-C/cnSGW sends Sx Delete Session Request to the UPF.
15 The UPF sends Sx Delete Session Response to the source SGW-C/cnSGW.
16 The source SGW-C/cnSGW sends Delete Session Request to the MME.